
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    
</body>
<script>
    function ajax(url){
        return new Promise((resolve, reject)=>{
            let xhr = new XMLHttpRequest()
            xhr.open('get', url)//链接
            xhr.send()//发送资源
            xhr.onreadystatechange = function(){
                console.log(xhr)
                if(xhr.readyState === 4){
                    if(xhr.status >= 200 && xhr.status < 300){
                        xhr.responseText //json 字符串
                        resolve(res)
                    }else{
                        reject(xhr.responseText)
                    }
                }
            }

        })

    }
    ajax('./01.json')
    .then((res)=>{
        console.log(res);

    })
    .catch((err)=>{
        console.log(err);
    })
</script>
</html>

